Add support for attempting to get image synchronously

AsyncDisplayKit/ASNetworkImageNode.mm

@@ -49,6 +49,7 @@ static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
   
   BOOL _cacheSupportsNewProtocol;
   BOOL _cacheSupportsClearing;
+  BOOL _cacheSupportsSynchronousFetch;
 }
 @end
 
@@ -73,6 +74,7 @@ static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
   
   _cacheSupportsNewProtocol = [cache respondsToSelector:@selector(cachedImageWithURL:callbackQueue:completion:)];
   _cacheSupportsClearing = [cache respondsToSelector:@selector(clearFetchedImageFromCacheWithURL:)];
+  _cacheSupportsSynchronousFetch = [cache respondsToSelector:@selector(synchronouslyFetchedCachedImageWithURL:)];
   
   _shouldCacheImage = YES;
   self.shouldBypassEnsureDisplay = YES;
@@ -169,6 +171,19 @@ static const CGSize kMinReleaseImageOnBackgroundSize = {20.0, 20.0};
 - (void)displayWillStart
 {
   [super displayWillStart];
+  
+  if (_cacheSupportsSynchronousFetch) {
+    {
+      ASDN::MutexLocker l(_lock);
+      if (_URL && _downloadIdentifier == nil) {
+        UIImage *result = [_cache synchronouslyFetchedCachedImageWithURL:_URL];
+        if (result) {
+          self.image = result;
+          _imageLoaded = YES;
+        }
+      }
+    }
+  }
 
   [self fetchData];
   

AsyncDisplayKit/Details/ASImageProtocols.h

@@ -17,6 +17,19 @@ typedef void(^ASImageCacherCompletion)(UIImage * _Nullable imageFromCache);
 
 @optional
 
+/**
+ @abstract Attempts to fetch an image with the given URL from a memory cache.
+ @param URL The URL of the image to retrieve from the cache.
+ @discussion This method exists to support synchronous rendering of nodes. Before the layer is drawn, this method
+ is called to attempt to get the image out of the cache synchronously. This allows drawing to occur on the main thread
+ if displaysAsynchronously is set to NO or recursivelyEnsureDisplaySynchronously: has been called.
+ 
+ If `URL` is nil, `completion` will be invoked immediately with a nil image. This method *should* block
+ the calling thread to fetch the image from a fast memory cache. It is OK to return nil from this method and instead
+ support only cachedImageWithURL:callbackQueue:completion: however, synchronous rendering will not be possible.
+ */
+- (_Nullable UIImage *)synchronouslyFetchedCachedImageWithURL:(NSURL *)URL;
+
 /**
  @abstract Attempts to fetch an image with the given URL from the cache.
  @param URL The URL of the image to retrieve from the cache.

AsyncDisplayKit/Details/ASPINRemoteImageDownloader.m

@@ -29,6 +29,13 @@
 
 #pragma mark ASImageProtocols
 
+- (UIImage *)synchronouslyFetchedCachedImageWithURL:(NSURL *)URL
+{
+  NSString *key = [[PINRemoteImageManager sharedImageManager] cacheKeyForURL:URL processorKey:nil];
+  PINRemoteImageManagerResult *result = [[PINRemoteImageManager sharedImageManager] synchronousImageFromCacheWithCacheKey:key options:PINRemoteImageManagerDownloadOptionsSkipDecode];
+  return result.image;
+}
+
 - (void)fetchCachedImageWithURL:(NSURL *)URL
                   callbackQueue:(dispatch_queue_t)callbackQueue
                      completion:(void (^)(CGImageRef imageFromCache))completion